In the manufacture of insulated electric wire such as copper magnet wire, it is standard practice to test the wire to determine whether the elongation property of the wire meets manufacturing specifications. This is accomplished by clamping a sample length of wire in two holding devices spaced a predetermined distance apart, and then moving one of the holding devices relative to the other until the wire breaks. The elongation property of the wire is indicated by the distance traveled by the movable holding device relative to the fixed holding device.
The final mechanical properties of copper wire are significantly affected by its overall processing history. In a wire manufacturing process disclosed in our copending application Ser. No. 671,275, filed Nov. 13, 1984, copper wire of improved mechanical properties is obtained by cold drawing wire through a first series of dies to form an intermediate diameter wire, suitably annealing the intermediate diameter wire, and then cold drawing the intermediate diameter wire through a second series of dies to form a wire of a final desired diameter. This wire drawing process with an intermediate anneal produces copper wire which has the ability to be subsequently quickly annealed at relatively low temperatures in a final annealing step to give an end product of superior mechanical properties. This final annealing step is advantageously performed as an in-line continuous anneal in connection with an enamel applying and curing operation. However, the end product may have unacceptable mechanical properties if the intermediate anneal was incompletely or not performed. As a result, substantial quantities of finished wire products may be wasted.
Accordingly, it would be desirable to determine the eventual elongation property of a copper wire which has been cold drawn with an intermediate anneal by testing of the wire before it is subjected to the final in-line continuous anneal and coating operations. Determining the elongation property of copper wire at this intermediate stage of manufacture by known methods, however, is of no avail since there is no discernible difference between the elongation values of wire cold drawn with or without an intermediate anneal.